1. Field of the Invention
The present invention relates to camera equipment with a zoom function and auto-focus function and a method of controlling an optical lens system in the camera equipment.
2. Description of the Related Art
Most of conventional digital cameras are equipped with a zoom function and auto-focus function. In general, zoom lens used in a digital camera alters an object distance, at which an image of an object can be brought into focus (focused focal position), as a zoom position alters. When the zoom position alters with an object image kept in focus, the focus lens is controlled so as to move to a position corresponding to the object distance at the altered zoom position after the zooming operation has been completed.
Since the above controlling operation can bring an object image out of focus during the zooming operation, such controlling operation has a disadvantage that it is not proper for photographing a moving image. A method of solving the disadvantage is proposed, for example, in Patent Document #1, in which method a focus speed (moving speed of a focus lens) is increased or decreased centering around an ideal speed at which the focus lenses move precisely after the focused focal lens locus, on the basis of levels (contract rate) of high frequency components contained in a video (image) signal obtained during the zooming operation. This method restricts object-image defocusing of more than a certain level during the zooming operation, and keeps object-image defocusing within an allowable range during the zooming operation.
[Patent Document #1] Japanese Laid-open Patent Specification Hei 6-62299, Paragraphs [0037] to [0045]
In this method, however, high frequency components contained the video (image) signal are successively detected and the focus speed is frequently altered based on the detected high frequency components, which causes a serious problem that increases burden imposed on the camera equipment (specifically, control unit in a micro computer) performing the above operation during the zooming operation.
The present invention has been made in consideration of the above problems, and it is an object of the present invention to provide camera equipment, a method of controlling an optical lens system in the camera equipment, and a program for performing the method, which is capable of keeping defocus of an object image within an allowable range by a simple control operation.